It has been previously
known that a quasi-decadal oscillation (QDO) of the tropical and subtropical
lower stratosphere exists and that this long-term variation has been
approximately in phase with the 11-year solar cycle during the period for which
accurately calibrated data are available.Evidence for the QDO is seen in both long-term column ozone records
(e.g., TOMS/SBUV) and meteorological records (e.g., NCEP reanalysis temperature
data).However, a solar cause of the QDO
has been controversial in part because of the small number (approximately 4) of
solar cycles for which global calibrated data are available.Empirical attribution of causal mechanisms
has also been difficult because a variety of solar-correlated phenomena (total
solar irradiance, Galactic cosmic ray flux, solar UV spectral irradiance, etc.)
all vary with the solar cycle.Here, we
report correlative evidence for thermal responses of the tropical upper
troposphere and lower stratosphere to solar UV variations occurring on the time
scale of the solar rotation period.While small in amplitude, the reality of the detected responses can be
verified because of the large number of 27-day cycles available for analysis
during two successive solar maximum periods.Also, because short-term variations of solar UV flux, total solar
irradiance, and Galactic cosmic ray flux differ significantly on the solar
rotation time scale, it is possible to specifically identify the UV flux as the
solar-correlated quantity that is most probably responsible for the observed
responses.It is expected that detailed
studies of the observed effects of short-term solar forcing in the tropical
lower stratosphere and upper troposphere will result in a better understanding
of the origin of the observed QDO.